The invention relates to a process for actualizing efficient production of a polyphenylene ether.
When a polyphenylene ether is obtained by reacting a phenol compound with oxygen in the presence of a catalyst, water which is the final reductant of oxygen is generated by polymerization. This water often induces hydrolysis of the catalyst and reduces its activity, which disturbs an increase in the molecular weight of the polyphenylene ether. Several proposals have been made for keeping the activity of the catalyst. The first proposal for maintaining activity while retaining water in the system is to use a quaternary ammonium salt as described in JP-B-59-22736 (The term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) or U.S. Pat. No. 4,042,564. Use of such an additive increases a cost, though its amount is not so large. The second proposal is to solubilize water by using a solvent which has compatibility therewith. This process is well known in the art. As the solvent, methanol is often employed. The polyphenylene ether obtained using a solvent system composed solely of methanol has however too low molecular weight to draw attentions as an industrial product. Since the solvent, such as methanol, having compatibility with water is often a poor solvent for a polyphenylene ether, precipitation of it occurs while its molecular weight is still low. Thus, the molecular weight cannot be increased as is expected. A polyphenylene ether is therefore often produced in a mixed solvent system containing a solvent having compatibility with the polyphenylene ether. This however requires complex solvent-collecting equipment. The third proposal is to impart the catalyst itself with water resistance. A process slightly improved in water resistance of the catalyst can be found in U.S. Pat. Nos. 4,028,341, 4,092,294 or 4,788,277, but in such a process, the catalyst has not yet acquired complete water resistance. For discharging water out of the system, conventionally employed are (most of them are well known in the art) addition of a dehydrating agent such as magnesium sulfate to a polymer mixture, use of molecular sieves, and the like (JP-B-44-27831). By removing water, the activity of the catalyst can be maintained. In U.S. Pat. No. 4,477,649, described is removal of water by centrifugal separation or decantation after a desired conversion ratio is attained by continuous polymerization of a polyphenylene ether and in Example 1 of this publication, supplementation of a catalyst component after centrifugal separation of reaction water is described. Although such a process is effective for raising the molecular weight of a polyphenylene ether, it is accompanied with such a drawback that a loss of the catalyst component caused by discarding of it upon centrifugation of reaction water must be made up for and this increases the cost. Particularly in the polymerization using a solvent having no compatibility with water, induction of phase separation of water is most important, but it has not yet been fully attained.
An object of the present invention is to provide an effective removing method of water generated upon production of a polyphenylene ether by reacting oxygen with a phenol compound in the presence of a catalyst, thereby providing a highly efficient production process of the polyphenylene ether.
Other objects and effects of the present invention will become apparent from the following description.
The present inventors carried out an extensive investigation with a view to overcoming the above-described problems. As a result, to their surprise, it was found that in the production process of a polyphenylene ether by using a specific catalyst, marked advantages are brought about by controlling the absolute pressure of the reaction system, oxygen partial pressure of the feed gas and oxygen concentration of the feed gas, thus leading to the completion of the invention.
That is, the above-described objects of the present invention have been achieved by providing the following production processes.
1) A process for producing a polyphenylene ether by oxidative polymerization of a phenol compound using a catalyst and an oxygen-containing gas,
wherein the catalyst comprises a copper compound, a bromine compound, a diamine compound represented by the following formula (1): 
(wherein, R1, R2, R3 and R4 each independently represents hydrogen or a C1-6 linear or branched alkyl group with the proviso that all of them do not represent hydrogen simultaneously, and R5 represents a linear or methyl-branched C2-5 alkylene group), a tertiary monoamine compound and a secondary monoamine compound,
wherein the process comprises the steps of:
controlling an absolute pressure at a gaseous phase of a reaction vessel to a range of from 0.098 MPa to less than 0.392 MPa; and
feeding the oxygen-containing gas to the reaction vessel, the oxygen-containing gas having an oxygen partial pressure, in terms of an absolute pressure, of from 0.0147 MPa to 0.0883 MPa.
2) The process according to item 1) above, wherein the oxygen-containing gas has an oxygen concentration of not greater than 21 vol. %.
3) The process according to item 1) above, wherein the oxygen-containing gas has an oxygen concentration of not greater than 11.6 vol. %.
4) The process according to any one of items 1) to 3) above, wherein the phenol compound is charged, at such a rate that charging of the whole amount thereof is completed within a period of from 10 minutes to less than 110 minutes, into the reaction vessel containing the catalyst components and being fed with the oxygen-containing gas.
5) The process according to item 4) above, wherein the oxygen-containing gas is fed at a rate ranging from 0.5 Nl/min to 15 Nl/min with respect to 1 kg of the reaction mixture at which the whole amount of the phenol compound is charged completely.
With the features as described in items 2) to 4) above, further desirable results can be obtained in the present invention.
The invention is described in more detail below.
The phenol compound to be used in the invention is a compound having a structure represented by the following formula (2): 
(wherein, R6 represents an alkyl, substituted alkyl, aralkyl, substituted aralkyl, aryl, substituted aryl, alkoxy or substituted alkoxy group, R7 represents, in addition to those described for R6, a halogen atom, and R8 represent, in addition to those described for R7, hydrogen). Examples of such a compound include 2,6-dimethylphenol, 2,3,6-trimethylphenol, 2-methyl-6-ethylphenol, 2,6-diethylphenol, 2-ethyl-6-n-propylphenol, 2-methyl-6-chlorophenol, 2-methyl-6-bromophenol, 2-methyl-6-isopropylphenol, 2-methyl-6-n-propylphenol, 2-ethyl-6-bromophenol, 2-methyl-6-n-butylphenol, 2,6-di-n-propylphenol, 2-ethyl-6-chlorophenol, 2-methyl-6-phenylphenol, 2,6-diphenylphenol, 2,6-bis-(4-fluorophenyl)phenol, 2-methyl-6-tolylphenol and 2,6-ditolylphenol. They may be used either singly or in combination. Incorporation thereto of a small amount of phenol, o-cresol, m-cresol, p-cresol, 2,4-dimethylphenol or 2-ethylphenol does not cause any substantial problem. Above all of these phenol compounds, 2,6-dimethylphenol is industrially important.
As a catalyst to be used upon production of a polyphenylene ether by oxidative polymerization of a phenol compound by using a catalyst and an oxygen-containing gas, a catalyst system comprising a copper compound, a bromine compound, a diamine compound represented by the following formula (1): 
(wherein, R1, R2, R3 and R4 each independently represents hydrogen or a C1-6 linear or branched alkyl group with the proviso that they do not represent hydrogen simultaneously, and R5 represents a linear or methyl-branched C2-5 alkylene group), a tertiary monoamine compound and a secondary monoamine compound must be used. It was found that in the production process using this catalyst, remarkable activity improving effects are brought about within a pressure range and oxygen partial pressure range as specified by the present invention. This phenomenon is so surprising as to exceed usual expectation.
Examples of the copper compound and of the bromine compound for use in the present invention are enumerated below.
As the copper compound, a cuprous compound and a cupric compound and a mixture thereof can be used.
Examples of the cuprous compound include cuprous oxide, cuprous chloride, cuprous bromide, cuprous sulfate and cuprous nitrate, while those of the cupric compound include cupric chloride, cupric bromide, cupric sulfate and cupric nitrate. Among them, cuprous oxide, cuprous chloride, cupric chloride, cuprous bromide and cupric bromide are preferred. These copper salts may be obtained upon use by the synthesis of an oxide, carbonate or hydroxide of copper and a corresponding halogen or acid. For example, such a copper salt is available by mixing cuprous oxide and hydrogen bromide (aqueous solution thereof). As the copper compound, cuprous compounds are particularly preferred. These copper compounds may be used either singly or in combination.
Examples of the bromine compound include hydrogen bromide, sodium bromide, potassium bromide, tetramethylammonium bromide and tetraethylammonium bromide. These compounds may be used as an aqueous solution or a solution in a suitable solvent. These bromine compounds may be used singly or in combination.
The most preferred combination of the copper compound and the bromine compound is that of cuprous oxide and an aqueous solution of hydrogen bromide. Although no particular limitation is imposed on the amount of them, they are used so that bromine atom is at least 2 times the mole but not greater than 10 times the mole of copper atom and copper atom falls within a range of 0.02 to 0.6 mole based on 100 moles of the phenol compound.
Examples of the secondary monoamine compound include dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine, di-n-butylamine, di-i-butylamine, di-t-butylamine, dipentylamines, dihexylamines, dioctylamines, didecylamines, dibenzylamines, methylethylamine, methylpropylamine, methylbutylamine and cyclohexylamine. Examples of the N-(substituted or unsubstituted phenyl)alkanolamine include N-phenylmethanolamine, N-phenylethanolamine, N-phenylpropanolamine, N-(m-methylphenyl)ethanolamine, N-(p-methylphenyl)ethanolamine, N-(2xe2x80x2,6xe2x80x2-dimethylphenyl)ethanolamine and N-(p-chlorophenyl)ethanolamine. Examples of the N-(hydrocarbon-substituted)aniline include N-ethylaniline, N-butylaniline, N-methyl-2-methylaniline, N-methyl-2,6-dimethylaniline and diphenylamine. These secondary monoamine compounds are however not limited to these examples. They may be used either singly or in combination. Although no particular limitation is imposed on the amount, it is usually added in an amount ranging from 0.05 to 15 moles based on 100 moles of the phenol compound.
The diamine compound to be used in the invention has a structure represented by the following formula (1): 
wherein R1, R2, R3 and R4 each independently represents hydrogen or a C1-6 linear or branched alkyl group, with the proviso that they do not represent a hydrogen atom at the same time, and R5 represents a C2-5 linear or methyl-branched alkylene group).
Among the diamine compounds having the above-described structure, N,Nxe2x80x2-di-t-butylethylenediamine is preferred. Although no particular limitation is imposed on the amount of the diamine compound, it is preferably added in an amount of at least 0.5 time the mole of the copper atom to be ordinarily used. The upper limit is not critical.
As the tertiary monoamine compound, aliphatic tertiary amines including alicyclic tertiary amines can be used. Examples include trimethylamine, triethylamine, tripropylamine, tributylamine, triisobutylamine, dimethylethylamine, dimethylpropylamine, allyldiethylamine, dimethyl-n-butylamine, diethylisopropylamine and N-methylcyclohexylamine. These tertiary monoamines may be used either singly or in combination. Although no particular limitation is imposed on the amount of it, an amount ranging from 0.1 to 15 moles relative to 100 moles of the phenol compound is preferred.
Although there is no particular limitation imposed on the nature of the solvent to be used in the invention insofar as it is not easily oxidized compared with the monomer to be oxidized and at the same time, has almost no reactivity with various radicals which are presumed to be formed during reaction, those permitting dissolution therein a low-molecular-weight phenol compound and also a portion or whole of the catalyst mixture. Examples of such a solvent include aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, hydrocarbon halides such as chloroform, methylene chloride, 1,2-dichloroethane, trichloroethane, chlorobenzene, dichlorobenzene and trichlorobenzene; and nitro compounds such as nitrobenzene. They may be used as a good solvent for the polymer. Examples of the poor solvent for the polymer include aliphatic hydrocarbons such as pentane, hexane, heptane, cyclohexane and cycloheptane and ethers such as tetrahydrofuran and diethyl ether.
A solvent having compatibility with water can be mixed in an amount not disturbing the advantages of the present invention. Examples of such a solvent include alcohols such as methanol, ethanol and propanol, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and ethyl formate, amides such as dimethylformamide and sulfoxides such as dimethylsulfoxide. These solvents may be used singly or if necessary, as a mixture.
The solvent to be used in the present invention exhibits particularly desirable activity under the conditions substantially free of compatibility with water. Aromatic hydrocarbon solvents such as toluene and xylene are frequently employed as a solvent.
The polymerization method becomes solution polymerization at a specific ratio of good solvent to poor solvent for a polyphenylene ether which is a polymer available by oxidative polymerization of a phenol compound. At an increased ratio of a poor solvent, on the other hand, the method becomes precipitation polymerization wherein the polymer is precipitated as particles in the reaction solvent with the progress of the reaction.
The invention is attained by using the above-described catalyst, controlling the absolute pressure at the gaseous phase portion of the reaction vessel to a range of from 0.098 MPa (mega pascal) to less than 0.392 MPa, and feeding a reaction vessel with an oxygen-containing gas having an oxygen partial pressure, in terms of an absolute pressure, of from 0.0147 MPa to 0.0883 MPa.
The oxygen concentration range of the oxygen-containing gas to be used in the invention is defined by the absolute pressure at the gaseous phase portion of the reaction vessel and oxygen absolute partial pressure of the oxygen-containing gas. In the present invention, when the absolute pressure at the gaseous phase portion of the reaction vessel is controlled to a range of from 0.098 MPa (mega pascal) to less than 0.392 MPa, the partial pressure of oxygen contained in the oxygen-containing gas fed to the reaction vessel must be from 0.0147 MPa to 0.0883 MPa in terms of an absolute pressure. The calculation formula for attaining such a state will next be described. Supposing that the absolute pressure at the gaseous phase portion of the reaction vessel is A(MPa), A falls within a range of 0.098xe2x89xa6A less than 0.392. The lower limit of the oxygen concentration in the oxygen-containing gas is represented by [(0.0147/A)xc3x97100] (%), while the upper limit of it is represented by [(0.0883/A)xc3x97100] (%). When the oxygen concentration is high, an inert gas must be introduced to the gaseous phase portion of the reaction vessel for safety. At this time, the higher the oxygen concentration of the oxygen-containing gas, the greater the amount of the inert gas to be introduced. It is therefore necessary to determine the upper limit of the oxygen concentration in consideration of an economical aspect. An oxygen concentration of 21 vol. % or less is preferred. Oxygen concentrations not greater than this value can improve the cost because the amount of an inert gas to be introduced into the gaseous phase portion of the reaction vessel can be decreased largely. Oxygen concentrations of 11.6 vol. % or less being more preferred and within this, safety is essentially ensured. Absolute pressures of 0.392 MPa or greater at the gaseous phase portion of the reaction vessel are not preferred, because they need inappropriately large equipment.
As the oxygen-containing gas in the invention, usable is that prepared by mixing oxygen and an inert gas to give its oxygen concentration within the range of the invention, air or a mixture of air and an inert gas. As the inert gas, any inert gas can be used insofar as it has not a large influence on the polymerization reaction. Nitrogen is the typical example of it.
The polymerization, feeding of the oxygen-containing gas and treatment of an unreacted gas can usually be carried out as follows: The absolute pressure at the gaseous phase portion in the reaction vessel having therein a catalyst mixture is adjusted to a range of from 0.098 MPa (mega pascal) to less than 0.392 MPa by introducing a gas (ex. inert gas or air-oxygen-containing gas, or mixture thereof). Gas-liquid mixing is then conducted by introducing an oxygen-containing gas having an oxygen partial pressure, in terms of an absolute pressure, of from 0.0147 MPa to 0.0883 MPa from a sparger attached at the bottom of the reaction vessel and stirring the mixture in the reaction vessel by an agitating element. When the oxygen concentration is 11.6% or greater, the gaseous phase portion is purged with nitrogen for safety. Polymerization reaction is then initiated by adding the phenol compound (or a solution having the phenol compound dissolved therein) to the reaction vessel through a pump. The gas-flow mixture discharged from the reaction vessel is cooled and condensed by a cooler disposed on the upper part of the reaction vessel. The condensate is introduced into a decanter, where it is separated into a water phase and an organic phase. The organic phase thus separated is returned back to the reaction vessel. The pressure of the reaction vessel is controlled by a control valve disposed downstream of the cooler. It is also possible to measure the oxygen concentration in the gas discharged from the cooler, mix the gas with oxygen, air or an inert gas, thereby controlling the oxygen concentration and absolute pressure to fall within the range of the invention, and then circulate the mixture to the sparger at the bottom of the reaction vessel. This makes it possible to decrease the amount of the mixture to be discharged to the environment and is therefore preferred. In the above-described operation, although no particular limitation is imposed on the addition rate of the phenol compound, a rate permitting completion of the charging of the whole amount within a period of from 10 minutes to less than 100 minutes is preferred. It is also possible to charge a portion of the phenol compound in the reaction vessel before introduction and feeding of the oxygen-containing gas and add the remaining portion at any time later or to charge in the reaction vessel the whole amount of the phenol compound in advance. In this case, the time when the oxygen-containing gas is introduced is regarded as the reaction starting point.
Although there is no particular limitation imposed on the introduction rate of the oxygen-containing gas, the feeding rate with respect to 1 kg of the reaction mixture at which charging of the whole amount of the phenol compound is completed preferably ranges from 0.5 Nl/min to 15 Nl/min. This amount is not critical, but at an excessively small amount, it takes long time to attain a desired molecular weight, thereby deteriorating productivity. Excessively large amounts, on the other hand, induce enlargement of equipment or increase of an exhaust gas amount so they are economically disadvantageous. During polymerization, the introduction rate can be changed. Favorable results are sometimes available by suppressing the introduction rate in the former stage of polymerization and by increasing it in the latter stage.
In the present invention, incorporation of a tetraalkylammonium salt compound, polyethylene-glycol-containing alkylamine or polyethylene-glycol-containing alkyl ammonium salt compound in the whole mixture charged in the reaction vessel in an amount not exceeding 0.1 wt. % is preferred for further improving the action of the invention, but it is not always necessary. Such a compound has a structure represented by the following formula (3), (4) or (5): 
(wherein R9, R10, R11 and R12 each independently represents a C1-22 linear or branched alkyl group and X represents a counter anion); 
(wherein R13 represents a C1-22 linear or branched alkyl group, R14 represents, in addition to those described for R13, a group represented by xe2x80x94(CH2CH2O)nxe2x80x94H (n stands for an integer of 1 to 40), and R15 is a group represented by xe2x80x94(CH2CH2O)nxe2x80x94H (n stands for an integer of 1 to 40)); 
(wherein R16 and R17 each independently represents a C1-22 linear or branched alkyl group, R18 represents, in addition to those described for R16, a group represented by xe2x80x94(CH2CH2O)nxe2x80x94H (n stands for an integer of 1 to 40), R19 is a group represented by xe2x80x94(CH2CH2O)nxe2x80x94H (n stands for an integer of 1 to 40)), and X is a counter anion).
The typical examples of such a compound include trioctylmethylammonium chloride known as a trade name of Aliquat 336 (product of Henkel KGaA) or Capriquat (product of Dojindo Laboratories). They are preferred in the present invention.
Polymerization is preferably effected at a temperature ranging from 0 to 80xc2x0 C., more preferably 10 to 60xc2x0 C., because reaction does not proceed smoothly at an excessively low temperature, while the catalyst happens to be deactivated at an excessively high temperature. Favorable results tend to be available by setting the temperature a little lower in the former stage of polymerization and a little higher in the latter stage of polymerization.
Reaction is terminated when the molecular weight reaches a desired value, because the molecular weight of the polymer is apparent from the viscosity of the polymer solution measured during polymerization or by the analysis of the sampled polymer.
No particular limitation is imposed on the treatment after completion of the polymerization reaction. A polyphenylene ether can usually be collected simply by adding an acid such as hydrochloric acid or acetic acid, ethylenediaminetetraacetic acid (EDTA) or salt thereof, or nitrilotriacetic acid or salt thereof to the reaction mixture to deactivate the catalyst, separating the resulting polymer from the reaction mixture, washing it with a solvent such as methanol which does not dissolve therein the polymer and then drying.